Voltage regulator

Voltage

Engineering

Transient (computer programming)

Materials science

Transient response

Low-dropout regulator

Digital control

NMOS logic

Operating system

Computer science

Capacitor

NAND gate

Transistor

Mathematics

Logic gate

Electronic engineering

Loop (graph theory)

Combinatorics

Dropout voltage

CMOS

Optoelectronics

Electrical engineering

IEEE Transactions on Circuits and Systems I Regular Papers

This paper presents an NMOS digital low-dropout regulator (LDO) with fast transient response and ultra-low quiescent current, to provide a tunable power supply for near-threshold voltage computing circuits in internet-of-things (IoT) devices. An LDO with an NMOS power transistor can enjoy the intrinsic fast transient response of the source-follower-like power stage, contributing to the proportional (P) part of the control loop. A shift-register-based digital control serves as an excellent candidate for the integral (I) part of the control loop. In addition, we propose a NAND-gate-based high-pass analog path (NAP) as the derivative (D) part of the loop, making the whole control scheme a complete PID control, therefore, achieving a fast transient response. We fabricated two versions of the prototype chip, one with a 35 pF on-chip load capacitor and a fast-transient on-chip load, and the other with no load capacitor, in 28-nm CMOS. The proposed NMOS digital LDO with NAP can handle the load transient of 160 mA/ns with 810-nA quiescent current, achieving 117-mV voltage undershoot. With the proposed techniques, we can achieve nearly two orders of better FoM when comparing it to the state-of-the-art works.

An NMOS Digital LDO With NAND-Based Analog-Assisted Loop in 28-nm CMOS